This invention relates to a movable contact assembly for an electric switch.
FIGS. 1 and 2 show in sectional views one example of a movable contact assembly for use in an electromagnetic contactor of the type disclosed in U.S. Pat. Nos. 4,450,328 and 3,320,392. In the figures, an electrically insulating, linearly-movable contact holder 1 of a conventional movable contact assembly has a movable contact arm 2 held in a through hole 1a formed in the holder 1. A stationary contact assembly 6 is provided opposite the movable contact assembly and includes the stationary contact elements 6a on both sides.
The movable contact arm 2 is made of an electrically conductive elongated rigid sheet having movable contact elements 2a mounted on its opposite ends. The movable contact arm 2 generally resembles section of a shallow dish having a flat central portion 2b. From each of the opposite ends of the central portion 2b, an upwardly inclined portion 2c extends at an angle to form, together with the flat central portion 2b, a shallow "U". A horizontal outer portion 2d carrying thereon a movable contact element 2a extends from the outer ends of each of the inclined portions 2c parallel to the flat central portion 2b.
The movable contact holder 1 has within its through hole 1a a downward projection 1b and a flat support surface 1c on which the flat central portion 2b of the movable contact arm 2 is placed. The movable contact arm 2 is resiliently held in place by a compression spring 4 disposed between the downward projection 1a and a spring retainer 3 positioned in the central portion 2b of the movable contact arm 2. The spring retainer 3 is provided with rounded lower corners which fit the corners or bent portions between the flat central portion 2b and the inclined portions 2c as shown in FIG. 1.
During assembling of the movable contact assembly, if the movable contact arm 2 is mislocated or placed in the slanted position in the through hole 1a of the contact holder 1 by a certain predetermined amount, the compression spring, together with the guiding action between the spring retainer 3 and the U-shaped configuration of the movable contact arm 2, act to automatically return the movable contact arm 2 to its proper position shown in FIG. 1.
However, when the misplacement exceeds a predetermined amount, the movable contact arm 2 can easily become caught in the position shown in FIG. 2, in which the movable contact arm 2 slants with respect to the contact holder 1 and engages with the holder 1 at one of the corners of the "U" and the movable contact element 2a, and the movable contact arm 2 is held in this displaced position by the action of the compression spring 4 through the spring retainer 3 which engages with the movable contact arm 2 at its corners.